Backlash eliminator



April 2, 1940. E. A. -PARSONS 2,195,799v

BCKLASH ELIMINATOR l Filed March 10, 1959 Patented Apr. 2., 1940 v UNITED STATES PTENT oFFlcE BAcxLAsn ELIMmATon Fred A. Parsons, Milwaukee, Wis'., assignor to Kearney & Trecker Corporation, West Allis,A Wis., a corporation of Wisconsin Application March 10,

' 16 claims.

nut means which require a'certain 'amount of.

desirable to eliminate all clearance or lost motion which might result in backlash, both between the screw and its nut and also between the nut and thesupport. Y

Most or all of the machines where it is desirable to eliminate backlash during the cutting movements have, in addition to the cutting movements, relatively very rapid vidle or quickhigh load at a high traverse speed. Nevertheless, the backlash elimination, to be fully effective should be operative before the cutting feed is engaged as. for example, beforeeffecting a change from a forward quick traverse to a for--l friction during hand operation of the supports.

A purpose of the invention is to provide backlash elimination means of improved form, particularly for screw and nut means.

lash eliminating` means in a `forme particularly vadapted for the drive of support movements, particularly of machine tools.

backlash eliminator which will operate without setting up undue frictional( resistance to the relative movement'of theparts between which it operates.

55 Another purpose is to provide an improved ward feed rate, particularly for climb cutting. It is also desirable that there should be no undue A further purpose is to provide improved back-j A further purpose is to provide an improved.

1939, Serial No. 260,983

(Cl. 'i4-441) backlash eliminator for machine tool supports which operates effectively under all cutting conditions, while avoiding the necessity for interlocksfor unloading or relieving the pressure or. friction of the backlash eliminator device during E5 other conditions of operation, andstill other objects will be apparent from what follows. l

The invention comprises the construction and combination of parts herein illustrated, de-

scribed and claimed and, since modifications are 10.v

contemplated, also includes such modifications as are equivalent to the structure of the claims.

The same parts havebeen identiiied by the same reference characters throughout, and in.- the drawing: A `l Fig. 1 shows nut and rotary screw means to which the invention has been applied in one of its simpler aspects.

Fig. 2 shows another form of' the invention, also in connection with a nut and rotary screw. 20

Fig. 3- shows the invention in connection with a rotary nut and stationary screw device, being otherwise similar to Fig. 2.

In the device of Fig. 1 a nut portion Il l is fixed in a bore II of a support I2 by the means 25 of ,a locking pin I3. Another nut portion I4 is l l relatively adjustable in the threaded bore l5, there being a pilot screw I6 vadapted to engage any of several arcuately closely spaced conilgurations, suchl as I1, I1, and aclamp screw I8. A 30 feed screw I9 engages both ofthe nut portions Ill, I4, and the nut portion I4 may be rotated to draw the feed screw to the left in Fig.. 1 y' against the abutment offered by the engaging threads of the nut 'portion I0, and the nut por- 35 tion I4 then locked in such position that there is a slight clearance forming a helical groove at the left of the screw abutment portions ofthe nut portion I0, as at, I 0a, and a slight clearance vfornling'a helical groove. -at the right of the 40 screw abutment portions 'of the nut portion I4, as at Ila. It will be understood that the actual clearances at Illa and Ma are much enlarged in the drawing. There will also be a very slight clearance forming very small helical grooves in 46 -each ofthe. nut portions at the othernside of the abutment. This istoo small to be shown in the drawing, but is indicated at lob and; Mb, being the running clearance which, as will be -uncler- K stood, is unavoidable where a screw is to turn in 50 l a nut.

Liquid, suchv for example as lubricating 011,. from a suitable pressure source, is continuously supplied to the space between the inner adja- K cent ends of the jnut portions I0', I4 through a 55 .the sleeve bore 33a.

piperchanel zo and armed channels 2|, 22, 2a,

and maintains the lhelical grooves such as I 0a, |017, I4a, |4b continuously iilled with liquid. If

screw i9' is moving any object, such as a ma-l chine tool table, then thethrust will cause the running clearance to be taken' up either at I0b or at |4b, according to the thrust direction, and the helical groove at the other point will be cor` respondingly larger but will nevertheless be lled with liquid.`

A check valve 24 continuously prevents return flow of oil to the pipe andthe oil ln the helical grooves canonly escape by following outwardly along the restricted helical paths. to end of the nut. Due tothe incompressible nature of the liquid and to the friction.. of the liquid in the helical passages such escape is Vsuflciently slow -even under heavy pressure o'r reversal of pres-v sure to avoid damage or sudden movement such as .might otherwise be caused, for example by reversal of thrust in climb-cutting in amilling machine, and more than suflicient to damp out any vibratory movement-or chatter, particularly since each half 'cycle of chatter or vibration will draw i'n more liquid throughthe check. valve to oppose the next half cycle in opposite direction.

The device just described is operative to eliminate backlash, but'only while a sufficiently close fit is maintained between theV screw and nut threads. The .device of Fig. 2 will operate to eliminate backlash substantially independently of the fit 'of the screw and nut parts, and 4without necessity for frequent adjustment of the running clearance, as follows:

A 'rotatable feed screw 25 engages two nut portions 25, 21 each closely slidably fitted ina bore 28 of a support -23, the nut portions beingr each prevented from rotating by slidably fitted keys s uch as 30, 3|. `Rigidly fixed in bore 28 by the means of locking pins 32, 32, there -is a sleeve 33, the nut portions 28,' 21 respectively having end portions 26a, 21a closely slidably fitted: in the bore 33a of the sleeve.- The construction provides I'he nut portion 26 is providedwith a fixed head 2Gb and the nut portion 21 withan ad. justing nut 44, threaded on nut portion 21 andloked in adjusted position by a screw 45. When the device is initially adjusted the nut 44 is adjusted until the head vportion 26h and the'adf iusting nut 44 are closely abutting the support 29 and there is only running clearance between the threads of feed screw 25A and nut portions 26, 21,

'as previously described for screw I I9. The nut portion. isthen locked screw 45.-

During use of the device of Fig. 2 the'liquid iills the chambers 34, A35 and urges' both of the nut portions 26, 21 outwardly. Any thrust on screw 25 seats either the head 2.612 or the-nut 44 solidly against the support to receive the thrust, and the other one of these parts moves outwardly by reason of the pressure ofthe liquid until such in adjusted position by voi? the bushingends in movement has taken upV all lost motion on the screw and also taken up all lost motion ofthe nut means relative to the support. A reversal of thrust cannot reversely shift the parts until some of the liquid has been displaced from behind the nut vportion, previously moved outwardly. Such displacement can onlyproc.eed very slowlythrough the closely tted sliding bores, and the resulting slow reverse movement ofthe part previously moved outwardly prevents vibration, chat- Moreover, upon any increment' terv or overrun. of such inward yielding of one nut portion the slack or clearance on the screw-is instantly taken up by outward movement of the other nut portion, which is not limited to slow4 movement but may move rapidly, whereby the device never has any lost motion, either between the screw and .the nutmeans, or between the nut means and thev support, no matter how'sudden may be the reversal of thrust,

Thus, if it be assumed, for example, that the thrust on screw 25 tends t'o move the screw aX-- ially in the direction of the arrow there shown,

then the screw threads will thrust against the threadsof nut portion 26 until the head 26h is solidly abutting the right-hand end of. the support 29. The screw threads will then be contacting the nut threads .as at 26e, Fig.l 2, and

there will then be clearance or lost motion between thescrew-threads and nut threads at the other side of the screw thread as indicated at 26d.

The device of Fig. 2 is intended 'to prevent the screw from moving back through such lost motion or clearance space inra manner to prevent chatter or overrun. The screw having been -shifted to theleft, as described, the nut .portion 21 will be shifted t0 the left bythe 'iiuidvflow into chamber 34 until prevented from further movement by contact of the nut threads against Y thefscrew threads, as 'at 210,. and in this position of nut portion 21 the screw cannot-move to. the right, even if thel thrust lload is reversed;

luntil suiiicient time has elapsed for some of the incompressible liquid to flow out of the Vchamber 34 along' the closely fitt'edcnut bearings in the bore of support 29 and of sleeve 33. Such reverse movement, if itV takes place, will-be at relative y very slow rate, sufficiently slow to prevent chatter or overrun. It will be understood that,

in the opposite directionof normal load 1thrust on s'crew 25 it .will be the nut portion 21- which transmits the normal thrust to the support 23 and the. nut portion 26 which moves outwardly to prevent backlash" caused by'reversal of thrust, but otherwise the action will be as described. .It Will also be understood that the clearances shown in the drawing are, for clearness, considerably exaggerated.- l

If desired, the chambers 34, 35 may each be provided with air bleeder' devices,.such -as the small-bore tubes 46, .41, but since the construction and operation of such devices arewell known,

it will not be necessary to` explain the bleeders" in detail. 'Any gas in the chambers-34, 35 would provide resiliency detrimentalto. operation of the device but ordinarily the gas will be continuously -releasedthroughthe closely'iitted sliding Joints. It is tobe noted that-while the 'nut portion .I ,0.-

of the device of Fig. 1 is here shownv rigidly fixed with its support by the means of the pin i3, such nut portion may instead be slidably mounted and keyed, similarly to the nut portions 26, 21 of the device of Fig.- 2. In such case .the device of Fig. 1 will operate in the manner-previously.described but with a certain degree of automatic take-up .the sleeve.

of lost motion effected-by the axialmovement of v the nut portion' I0, 'as will. he understood from the.

description of the operation 'of the device of Fig. 2.

In thedevice of Fig. 3 a table screw-48 is suitablyno'n-rotatably supported and nut portions 26,

21, exactly similar to the correspondingly numbered nut portions previously described, are -ro'- tatable Vwith a 4sleeve 49 in a suitable bore in a support Alill. Sleeve 49 may be driven. -fromany suitable transmission, not shown, 'through a gear 5 I 4which in this instance `is formed integral with At the other end of the.sleeve 49 there is an' adjusting nut 52 which may be ad- It is to be 'noted-that, irrespective of the load, the outward pressure on the nut portions of Figs.

2, 3 need not be high in order for the device to operate to substantially eliminate backlash. The

vload thrust in .either direction is taken" against the -flxed abutment of the housing, and the pure pose of the outward pressure on the nuts is only to take up the clearance to prevent backlash.,

The device therefore operates suitably'for manual operation as well as for cutting and quick traverse movement and is subject to very little. wear, par

ticularly by reason of the lubrication through continuous -leakage of liquid to lubricate the' screw.

' But if the liquid pressure isnot sumcient to insure forcing the nutv portions outwardly to the limit .of their axial lmoyernenia such pressure should be supplied by other means, as for example by suitable springs, not shown. In suchA case the low pressure liquid will still operate tov prevent backlash, chatter and overrun, as described.

' -In each of the modifications here shownjthe structure operates lto provide a primary abutment means impositively resisting the thrust and displacement of the screw .and nut means relative to the support and comprising a body-of liquid confined to restrict leakage to a`re1atively slow rate, the primary abutment means operating to automatically take up any lost motion relative to the support. supplementingv the primary abut- .l

mentmeans there is, in each instance, a secondary abutment means acting to positively limit. the

movement relative to the support, following a rela?. leakage from 'the body of tively small amount of coniinedliquid. .v

It will be noted that the' devices described ere' operative to eliminateA backlash withot'objectlonable friction even where the lead .screw-has become considerably more worn in some axial portions than in others, the mechanism accommodating .itself without difliculty to such variations.

- What is claimed is: l

1. I n a means for reducing or eliminating backlash between two machine elements thecomb'i-v nationof members relatively movable in accordance with backlash between'said elements to increase the volume of a restricted space, means for 'supply of liquid to said space, and 4means preannular groove 49a and a drilled hole 49h.

at a relatively slow rate.

venting escape .of liquid from said vspace except 2. A backlash eliminator for machine mechain accordance withthe backlash in said mechanismto increase the volume of a restricted space,

. nism including two members relatively movable a source of pressure liquid,- means substantially freely admitting liquid -from said vlsource to said space, and restrictingmeans limiting outflow of liquid from said space to a relatively vslowA rate.

3. The combination of a feed screw, nutineans therefor including two nut portions relatively adjustable for eliminating backlash .of the nut means relative to saidscrew, means operative Afor the relative adjustment of said nutportions in the direction eliminating backlash, and means subsemovement of the adjusted nut portion while restricring the vrate thereof.

4. The combination of a feed screw, nutmeans therefor including 'two nut portions relatively adjustable for eliminating backlash of the nut means relative to said screw, means operative for 'said' relative adjustment of the nut portions inthe direction eliminating backlash including a piston, a cylinder and a liquid supply Source therefor, and means subsequently operative to limit the rate -of reverse adjustment of the Aadjusted nut portion .including a restricted outlet forliquid from said cylinder.

5. The combination of a feed screw, nut means quently operative to permit reverse direction -of therefor including two nut portions relatively axially adjustable, the threads of one of said nut portions contacting thescrew threads at -the one side thereof to prevent relative movement therebetween' in one axial direction, means 'opera'tive to axially relatively adjust said nut portions until the thread'sof the other nut portion contact said` screw threads at the other side thereof, and means subsequently-v operative to permit the reverse direction of adjustment of theadjusted nut portion while restricting the rate thereof. y

6. The combination of'a feed screw for relative I supportmovement, nut means for said feed screw including two -nut portions relatively axially adjustable, means operative to axially relatively adj'ust said nut portions until the nut-thread elements of the-l different nut portions respectively.

contact the `screwthreads on opposite axial sides thereof, andmeans subsequently operative to per-' mit reverse direction of adjustment of the i adjusted nut portion but only at restricted rate.

. 7. The combinationof a feed screw, nut means therefor. including two nut portions relatively.

axially adjustable,` 'the threads of one of said nute portions contacting thescrew threads at the one side thereofto prevent relative movement .therebetween in oneaxial direction, means operative to axially relatively adjust said nut. portions until the threads of the other nut portion Acontact said screw threads at the other side thereof, and means subsequently operative to permit the reverse" direction of adjustment of the adjusted vnut por tion including piston and cylinder meanshaving a restricted outlet limiting the rate of said reverseadjustment.

8. The combination of a feed screw, a support,

nut means for said screw including a-iirst .nut

portion, positive abutment means for said support and lrstnut portion limiting the relative movement therebetween in one direction axially of said screw, said nut means including a second nut portion movable in said direction, whereby to simultaneously eliminate lostmotion between said nut means and said screw and between said abutment means, means for movement of said second nut portion in said direction to eifect said lost motion elimination, and means subsequently operative to permit opposite movement of said second nut portion while restricting the rate thereof'.

9. The combination of a feed screw, a support, nut means for said screw including a first nut portion, positive abutment means for said support and first nut portion limiting the relative movement' therebetween in one direction axially of said screw, said nut means including a second nut portion movable in said direction, whereby to simultaneously eliminate lost motion between said nut means and said screw and between said abutment means, means for movement of said second nut portion in said direction to eiect said lost motion elimination, and means subsequently operative to permit the opposite movement of said second nut portion including piston and cylinder means having outlet restricting means limiting the rate of said opposite movements.

10. The combination of a feed screw, a lsupport,

nut means for said screw including rst and second nut portions relatively movable for elimi-- direction, said support and second 'nut portion providing positive abutment means limiting said movement of the second nut portion in the other direction, means for movement of each of said nut portions in a direction to separate the associated abutment means, and means subsequently permitting the opposite direction of movement of each of said nut portions while restricting the rate thereof.

11. The combination of a feed screw, a support, nut means for said screw including rst and second nut portions relatively movable for elimination oi' lost motion between the screw and the nut means, a support, said support and first nut portion providing positive abutment means limiting said movement of the mst nut portion in one direction, said support and second nut portion providing positive abutment means limitingl said movement of the second nut portion in the other direction, means for movement of each of said nut portions in a direction to separate the associated abutment means, and means subsequently operative to permit the opposite direction of movement oi' each of said nut portions including for each nut portion piston and cylinder means having outlet restricting means limiting the rate of said opposite direction of movement.

12. The combination of a support providing a bore, a feed screw extending in said bore, nut

means for said screw including first and second. nut portions each slidable in said bore andy spaced apart axially, said nut portions being relatively axially movable to eliminate axial lost motion between said nut means and said screw, means simultaneously urging each of said' nut portions in a direction to eliminate said lost motion, and means permitting movement of each of said nut portions in the opposite direction while restricting the rate of such opposite movement.

13. The combination of a support providing a bore, a feed screw extending in said bore, nut means for said screw including iirst and second nut portions each slidable in said bore and spaced apart axially, said nut portions being relatively axially movable to eliminatev axial lost motion between said nut means and said screw, means simultaneously urging each of said nut portions 1 in a direction to eliminate said lost motion, means permitting movement of each of said nut portions in the opposite direction while restricting the rate thereof, and means limiting the amount of said opposite movement of at least4 one of said nut portions relative to said support.

14. 'I'he combination of a support providing a bore, a feed screw extending in said bore, nut means for said screw including rst and second nut portions each slidable in said bore and spaced apart axially, said nut portions being relatively axially movableto eliminate axial lost motion between said nut means and said screw,

means simultaneously urging each of said nut portions in a direction to eliminate said lost motion, means permitting movement of each-of said nut portions in the opposite direction including foreach nut portion piston and cylinder means having outlet restricting means limiting the rate of movement in said opposite direction, and positive abutment means limiting the amount of said opposite movement of atA Aleast one of said nut portions relative to said support.

15. In a machine' tool having a support, and l thrust means including screw and nut' means associatedwith the support, the combination of thrust abutment means including primary abutmentmeans comprising a body of liquid opposing relative movement of said support and said screw and nut means and confined to restrict the rate of leakage thereof, and supplemental abutment means including said support and adapted to operate "as a positive abutment4 I opposing movement of said screw and nut means relative to said support after leakage of liquid from the body of liquid of said primary abutment means.

16. In a machine ltool having a support, andscrew and nut means relativeto said support after leakage of liquid from said confined body of liquid.

FRED A.- PARSONS.

CERTIFICATE 0F' coRREcTioN.

Patent No. 2,195,799. y April' 2,` 19m).

FRED A. PARSONS.

It is herebyy certified that error appears in the printed specification off the-abowrre mimbeed :ptent requiring oorrection as follows: Page )4., first column, line 29, claim 1Q, for the word and comma "means," read --me-ans fo-r; and that the said Letters Patent should be -read lwith this cor-'rection thereiniat the same may conform to the recordof the case 1n the Patent office. 1 n

signed and. sealed this Mtr; day of June, A. D. 191.0.

l v Henry Vari Arsdale, (Seal) Acting` Commissioner of Patents.l 

